To switch focus from one object to another during a film production is called focus pulling and it is known to provide focus pulling by means of a so called follow focus unit through which it is possible for an operator to control the focus of a camera, set the focus on an object and switch focus from one object to another. Modern follow focus units are handheld remote control units through which a turning mechanism on the camera is controlled, which turning mechanism controls the focus of the camera.
Traditionally the remote follow focus unit has some kind of turning knob where each position on the turning knob corresponds to a setting on the turning mechanism, and where the adjustment of the turning knob will cause a turn and adjustment of the turning mechanism and the focus control on the camera lens.
The operator makes manual measurements of distances from the main camera to different objects that are to be in focus and marks representing different objects and their focus distances are set on the turning knob to enable fast switching between different focus distances.
Each mark represents a setting on the turning knob and the pulling of focus from one mark to another is done manually. Fine tuning is also done manually with the same control.
The manual control enables the possibility to pull fast or slow which gives an artistic freedom to control the pulling process.
It is also known to control the aperture settings of the lens on the main camera by means of the remote control unit and the turning mechanism.
It is known to use a system to measure the distance to objects to be followed by the use of some kind of tag that is placed on the object and detected by the system. Patent publication WO 2015/073916 A2 shows a system for improved camera focusing systems using subject location tags, where the system comprises camera accessories and in-lens technologies that allows for the continuous, automated focus of a subject by measuring the distance between the camera and a subject that has been “tagged” with a locator beacon. It is required that each subject is tagged or marked by a beacon that is visible to the system at all times.
It is a problem to obtain required distance information to pull focus from one object to another and to find focus on the new object with accuracy, that is to find and set focus directly on the new object, even when a follow focus unit is connected to the camera where distances have been measured and are marked on the follow focus unit.
It is a problem to use an automatic system where distances are measured to objects to be followed by means of marking each object with some kind of beacon when objects are moving so that beacons are no longer visible to the system.
It is a problem to use beacons in applications where a shallow depth of field is used in the filming process since focus often is wanted on a person's eye while the beacon may be positioned in another distance as it is placed on a person's clothing or other part of the body.
Depending on the type of beacon, the use of distance measurements to beacons are often limited by lighting conditions and it is a problem to measure accurate distances in conditions such as bright sunlight or dark scenes. Accuracy also gets lower as the distance to the object increases.
It is a problem to provide automatic switching as well as manual switching, and a possibility to freely choose between automatic and manual switching of focus between objects.
It is also a problem to provide a remote follow focus unit that is easily operated and allow a user to hold and operate the control unit over long periods of time.
It is also a problem to provide an aid in manual focus through which an operator can know when he is approaching and finally reaching the correct focus distance.
It is a problem to provide a possibility to fine tune the focus distance to a selected object during filming.
It is also a problem to maintain focus on a moving object once focus has been set.
It is a problem to know distances to different objects and setting focus according to these distances during the filming process.
It is a problem to know distances to several objects, to keep track of these distances when one or several of the objects are movable, and to separate objects from each other while they are moving.